The TRS-80 series included a lot of other Non compatible models like the Model I, III, 4 and 4p, which were compatible somewhat with each other, and the Model II and 16 where were no where near compatible with the other ones.
The original ones used z80 cpus, while the color computers were 6809 cpu based.
All the original TRS-80 computers were also monochrome, the coco, brought us wonderful color.